Our research focuses on the molecular, cellular, and systemic mechanisms underlying the neural functions of glycoprotein sialylation. Although the brain is the organ with the most prominent sialylation in human body, and recent studies implicated sialylation defects in several neurological diseases, the functions of this important type of glycosylation in the nervous system are still poorly understood. The intricacies of glycosylation, increased pleiotropy and redundancy, and limitations of available genetic approaches significantly hinder the research on sialylation in the overwhelmingly complex vertebrate nervous system. Thus, a suitable model system would be an important tool for more efficient and accelerated studies in this area. Here we propose to use Drosophila as a model organism to investigate the neural functions of N-linked sialylation. We previously characterized Drosophila sialyltransferase, DSiaT, a sole sialyltransferase in Drosophila. This enzyme is highly homologous to its human counterpart which also shares with DSiaT several functional properties, including similar acceptor specificity and an elevated expression in the brain. Our recent experiments revealed that the function of sialylation in Drosophila is limited to the nervous system. We found that sialylation regulates neural transmission and the development of neuromuscular junctions. Abnormal sialylation results in Drosophila in prominent neurological phenotypes, including temperature-sensitive paralysis, defects in locomotion, and a significantly shortened life span. Our experiments indicated that a simple N-linked glycoprotein sialylation plays a prominent role in modulating neural activity, which establishes a new paradigm of the involvement of glycosylation in the nervous system regulation. This novel, nervous system-specific function of N-linked sialylated glycans is potentially conserved between flies and humans. The current project will extend our previous research and will investigate (i) the cellular mechanisms underlying the neural function of sialylation in Drosophila, (ii) the molecular mechanisms of sialylation-mediated control of neural excitability, and (iii) the role of sialylation in neural plasticity. We will use a multidisciplinary strategy, combining the advantages of Drosophila model system, including its exceptional amenability to genetic manipulations, exhaustively characterized neural development, low redundancy and pleiotropy of sialylation genes, with well-established electrophysiological and behavioral approaches, cell culture and biochemical techniques, as well as novel technologies for glycan analyses. This project will shed light on the crucial evolutionarily conserved principles of neural regulation and development, which could be useful for biomedical research and relevant therapeutic strategies. Our research will also establish Drosophila as a versatile model system for future studies of the role of glycosylation in the nervous system.